Responses to Heat and Cold Stress

Extreme environmental temperatures affect plant metabolism. Excessive heat denatures enzymes and other proteins, while extreme cold freezes intracellular water. How do plants respond to heat and cold stress?

When the ambient temperature is high, plants avoid excessive water loss by closing stomata during the day,  often at the expense of reduced CO2 uptake and photosynthetic activity.

Heat stress can also cause plant cells to synthesize large quantities of special proteins called heat shock proteins. They act as chaperones, helping other proteins fold into their functional shapes or protect enzymes and proteins from denaturation.

Plants adjust the lipid composition of their cell membranes to maintain integrity and optimal membrane fluidity in response to heat and cold stress. Membrane fluidity influences membrane permeability, which regulates the movement of molecules through the membrane and prevents leakage into or out of the cell.

Phospholipids, arranged in a bilayer, form the basic structure of the plasma membrane. The lipid component of this bilayer is composed of saturated or unsaturated fatty acids.

During heat stress, the high temperature causes the lipid bilayer to become more fluid and more permeable or leaky. Plants respond by increasing the proportion of saturated fatty acids in the membranes to improve heat resistance and prevent membrane fluidization.

During cold stress, the low temperature causes the lipid bilayer to become more rigid, decreasing permeability. In response, the proportion of unsaturated fatty acids in the membranes increases to reduce membrane rigidity and maintain optimal fluidity.

At sub-freezing temperatures, ice formation in the cell walls and intercellular spaces of most plants causes water to leave the cytoplasm, resulting in cellular dehydration. To prevent this, many frost-tolerant plants accumulate solutes, such as sugars, in their cytoplasm to regulate their osmotic potential.

Adaptive mechanisms in response to heat and cold stress help maintain homeostasis and ensure the survival of plants.